1. Field of the Invention
The present invention generally relates semiconductor structures, and in particular, conductors which may be used as electrical fuses and methods of making the same.
2. Description of Related Art
In the semiconductor industry, fuses are used in integrated circuits (ICs) for improving manufacturing yield or customizing generic integrated circuits. A fuse can be disconnected (known as “blowing a fuse”) by passing an electric current or by applying a laser to melt the fuse. A fuse blown by electric current is referred to as an electrical fuse (e-fuse). After blowing the fuse, it is considered programmed.
Programming an e-fuse can occur by passing enough current so that the fuse melts, or passing enough current so that electromigration takes place which either causes an open in the fuse element or increases the resistance.
E-fuses can have one of two orientations, horizontal or vertical. When viewed from top down, a horizontal e-fuse typically includes a line having two wide pad areas at either end with a thinner link in between and connecting the pad areas of the line. The wide pads are to make connections which provide current. Because the current density will be higher at the thin link, the fuse will blow at the thin link. The line is parallel to the substrate, thus a horizontal fuse. A horizontal fuse is typically made of polysilicon and a silicide and found on and in direct contact with the substrate, thus in the front end of line (FEOL) of an IC. However, a horizontal fuse may also be built from other materials and be located in the back end of line (BEOL) wiring levels of an IC. Generally, BEOL is considered to include the first metal level (M1) and above. In either location, the horizontal orientation of the fuse consumes valuable real estate on the chip. Furthermore, as ICs fabrication moves to replacement metal gate processes or FinFET configurations, fabrication of e-fuses in the FEOL becomes difficult to integrate.
A vertical e-fuse is located in the BEOL and when viewed in cross-section includes a top line level, a lower line level and a via connecting the two line levels. The vertical e-fuse is typically designed to blow in the via, but does not always reliably do so. One reason a vertical e-fuse may not reliably blow in the via is because in a dual damascene process there is relatively little resistivity difference between the metal lines and the via. A second reason a vertical e-fuse may not reliably blow in the via is because the larger dimensions of the BEOL (as compared to the FEOL) requires much higher programming current which can cause the fuse to blow away from the desired location.